OS Therapies, Inc. (NYSE-A: OSTX) has announced positive topline data from its Phase 2b clinical trial of OST-HER2 in patients with resected, recurrent osteosarcoma. The data, released in January 2025, indicates that OST-HER2 met its primary endpoint with statistical significance, offering a potential new treatment option for a disease with limited alternatives.
The Phase 2b trial enrolled 41 patients across 21 clinical trial sites in the United States. OST-HER2, a cancer immunotherapy biologic drug candidate, utilizes a bioengineered form of Listeria monocytogenes (Lm) to target HER2-expressing cancer cells, triggering a strong immune response. The trial focused on patients with recurrent, fully resected, lung metastatic osteosarcoma.
Efficacy and Safety Results
The primary endpoint, 12-month Event Free Survival (EFS), demonstrated a significant improvement in patients treated with OST-HER2 compared to a historical control group from published United States literature. According to the company, 33% of OST-HER2 patients were Responders vs. 20% in the Published Control. Furthermore, a greater proportion of OST-HER2 treated patients were alive at the post-Resection interim 12-month timepoint (91% vs. 80%) and 24-month timepoints (61% vs. 40%) than the Published Control, in the 3-year overall survival secondary endpoint. Notably, 100% of patients on OST-HER2 who were disease free at 12 months were alive at the 12-month, 18-month, 24-month and 30-month timepoints, as of each of their last dates of contact.
OST-HER2 was reported to be well-tolerated, with a safety profile that supports regulatory approval. These findings suggest that OST-HER2 could offer a meaningful clinical benefit for osteosarcoma patients who have limited treatment options after failure of first-line therapies.
Regulatory Pathway and Future Plans
OS Therapies is actively engaging with the FDA to discuss the regulatory path forward for OST-HER2. The company plans to request a meeting with the FDA in early Q2 2025 to review the data and discuss the Biologics License Application (BLA) submission. Provided positive feedback from the FDA, OS Therapies anticipates filing the BLA later in the second quarter of 2025, with potential approval within six months.
Paul Romness, MHP, Chairman & CEO of OS Therapies, stated, "The data we generated in our Phase 2b trial with OST-HER2 provides the first glimmer of hope in over 40 years that a paradigm shift could radically change the course of this deadly disease. We intend to stay laser focused on our mission of bringing this therapy to market."
Acquisition of Clinical Assets
In January 2025, OS Therapies announced an agreement to acquire certain clinical and intellectual property assets from Ayala. This acquisition includes rights to two new Listeria-based clinical-stage immunotherapy candidates: ADXS-503 for lung cancer and ADXS-504 for prostate cancer. The acquisition also reduces the company’s royalty rate from 10% to 1.5% of net sales and eliminates $16.5 million in milestones on the first $100 million in sales for OST-HER2 in osteosarcoma.
Financial Position
OS Therapies completed a $7.1 million financing round in January 2025, designed to fund the company through a potential BLA decision from the FDA regarding the OST-HER2 program. The company anticipates that approval of OST-HER2 for osteosarcoma on or before September 30, 2026, would grandfather into the FDA’s sunsetting Priority Review Voucher (PRV) program, potentially resulting in non-dilutive capital expected in the $150 million range.
